This invention relates to material handling systems, and more particularly to systems for periodically supplying batches of coke to a blast furnace.
In the operation of a blast furnace, a plurality of substances, viz. iron ore, fluxes and a source of carbon such as coke, is periodically supplied to the top of the furnace. The carbon in the coke reduces the iron ore and also provides the heat necessary for the chemical reactions in the furnace to take place. The main product of the furnace is iron; useful byproducts are slag and hot gases for heating in other processes.
In order to insure that the iron ore is substantially completely reduced, it is necessary to provide an excess of carbon to the furnace. However, too much of an excess results in wasted coke as well as iron having an improper chemistry; in addition, hot gases too rich in carbon are produced, and the composition of the slag is improper. For these reasons, it is desirable to closely control the amount of carbon in each batch of coke supplied to the furnace. Typically, a batch may consist of three weighings.
The coke which is supplied to the furnace, being naturally porous, contains moisture in varying amounts. Thus, weighing systems designed to provide constant weight batches of coke must be provided with means to compensate for the moisture in the coke. In addition, means must be provided to compensate for the inevitable errors in weight which occur from weighing to weighing due to overshoot, i.e., the additional amount of coke supplied to the weigh hopper after the coke shut-off signal has occurred.
In the past, attempts have been made to correct for moisture by measuring the moisture content of a sample of coke from a supply being fed to a delivery car, feeding this value to a computer, determining the corrected coke weight, and using this value for controlling the termination of supply to the car. However, no accurate means has been available for determining the moisture content of coke in a short enough period of time for this type of system to be satisfactory.
Attempts have been made to compensate for variations in overshoot by accumulating errors over a long period of time until a predetermined value is reached, at which time a compensatory amount of coke is supplied to the furnace. However, this type of system does not solve the problem of supplying a substantially correct amount of coke at each batch delivery, and this results in iron and byproducts of varying chemistry, and requires more total coke to be sure that the amount of coke does not go below the minimum required to keep the furnace operating.
It is an object of this invention to provide a system for supplying for each weighing of material a control signal which rapidly corrects for all moisture-based and weighing-based errors in prior weighings of material.